Alternating phase-shift mask inspection method and apparatus
First Claim
1. A method for inspecting a phase shift mask that is used with a photolithographic optical exposure system under a set of exposure conditions, said method comprising:
- acquiring a plurality of aerial images produced by said phase shift mask using a transmitted light, said plurality of aerial images being acquired in an aerial imaging inspection system and within a process window of said exposure system by emulating said set of exposure conditions;
said plurality of aerial images including a first and a second aerial image produced by said phase shift mask;
wherein said first aerial image produced by said phase shift mask is in a first out of focus condition, and said second aerial image produced by said phase shift mask is in a second out of focus condition; and
comparing said first and said second aerial images to each other to detect phase defects and errors in said phase shift mask, whereinsaid first and said second aerial images are concurrently produced from the same light transmitted by the mask; and
,wherein prior to said comparison step, said first and second aerial images are transformed to simulate a behavior of an exposure system and photoresist.
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Accused Products
Abstract
A reticle inspection system and method for complete and fast inspection of phase shift mask reticles, both for incoming inspection and for periodic and pre-exposure inspection tool, is employable by facilities such as mask shops as an inspection tool compatible to the mask shop'"'"'s customers. The inventive system and method detect phase errors in an aerial image by acquiring the image of the phase shift mask under the same optical conditions as the exposure conditions (i.e. wavelength, numerical aperture, sigma, and illumination aperture type). Images are acquired at a positive out-of-focus and a negative out-of-focus, and are compared in order to enhance possible phase error. The term “phase error” refers to the acceptable range of the phase deviation from the programmed 180° on the phase shift mask, by using the exposure system to achieve the image on the photoresist, satisfying the requirements of the wafer specification.
65 Citations
33 Claims
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1. A method for inspecting a phase shift mask that is used with a photolithographic optical exposure system under a set of exposure conditions, said method comprising:
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acquiring a plurality of aerial images produced by said phase shift mask using a transmitted light, said plurality of aerial images being acquired in an aerial imaging inspection system and within a process window of said exposure system by emulating said set of exposure conditions;
said plurality of aerial images including a first and a second aerial image produced by said phase shift mask;
wherein said first aerial image produced by said phase shift mask is in a first out of focus condition, and said second aerial image produced by said phase shift mask is in a second out of focus condition; andcomparing said first and said second aerial images to each other to detect phase defects and errors in said phase shift mask, wherein said first and said second aerial images are concurrently produced from the same light transmitted by the mask; and
,wherein prior to said comparison step, said first and second aerial images are transformed to simulate a behavior of an exposure system and photoresist. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An apparatus for inspecting a phase shift mask that is used with an optical exposure system under a set of exposure conditions, said apparatus comprising:
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a scanner for acquiring a plurality of aerial images produced by light transmitted through said phase shift mask while emulating said set of exposure conditions;
said plurality of aerial images generated by said phase shift mask comprising a first and a second aerial image generated by said phase shift mask;
wherein said first aerial image generated by said phase shift mask is in a first out of focus condition, and said second aerial image generated by said phase shift mask is in a second out of focus condition; andan image processing module for detecting variations in phase of said phase shift mask by, first transforming said first and second aerial images to simulate a behavior of an exposure system and photoresist and then comparing said first and said second aerial images generated by said phase shift mask to each other, wherein said first and said second aerial images are concurrently produced from the same light transmitted by the mask. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. An apparatus for inspecting a phase shift mask that is used with an optical exposure system under a set of exposure conditions, said apparatus comprising:
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a light source; transmission light illumination means for illuminating said phase shift mask; optical means for producing a plurality of magnified aerial images generated by said phase shift mask while emulating said set of exposure conditions, said optical means having a numerical aperture diaphragm for reproducing said set of exposure conditions; imaging means for acquiring said plurality of magnified aerial images generated by said phase shift mask;
said plurality of aerial images generated by said phase shift mask comprising a first and a second aerial images generated by said phase shift mask;
wherein said first aerial image generated by said phase shift mask is in a first out of focus condition, and said second aerial image generated by said phase shift mask is in a second out of focus condition; andimage processing means for analyzing a condition of said phase shift mask using said plurality of aerial images generated by said phase shift mask, wherein said first and said second aerial images generated by said phase shift mask are first transformed to simulate the behavior of an exposure system and a photoresist and then compared to each other and said first and said second aerial images are concurrently produced from the same light transmitted by the mask. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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Specification